The present invention relates to a mask suitable for use in forming a container in a substrate, and more specifically to a mask having a fine geometry, rectangular opening that may be utilized to etch a substrate and define an opening or hole therein having an outline corresponding to the rectangular opening of the mask. Additionally, the present invention relates to a container-cell capacitor for a dynamic random access memory (DRAM).
An exemplary prior art dynamic random access memory (DRAM) device comprises an array of container-cell capacitors that are formed in a substrate. In the current application, the term xe2x80x9csubstratexe2x80x9d or xe2x80x9csemiconductor substratexe2x80x9d will be understood to mean any construction comprising semiconductor material, including but not limited to bulk semiconductive materials such as a semiconductor wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). Further, the term xe2x80x9csubstratexe2x80x9d also refers to any supporting structure including, but not limited to, the semiconductive substrates described above.
One known container structure for the container-cell capacitors of a memory array, comprises a container having cylindrical or xe2x80x9cbath-tubxe2x80x9d shape. In a known method of fabricating a container in a substrate, with reference to FIGS. 1-3, a single layer of photoresist 12 is coated over layer 10 of, for example, borophosphosilicate glass (BPSG). Light 14, such as ultraviolet light, irradiates a select region 16 of photoresist 12 as determined by an exposure plate or reticle (not shown). Advancing to FIG. 2, photoresist 12 is developed to form opening 18. Opening 18 exposes surface 20 of layer 10. With this mask 12, layer 10 can be etched (e.g., by a reactive plasma etch) to form container 19 within layer 10, see FIG. 3. As used herein, the term xe2x80x9ccontainerxe2x80x9d shall be inclusive of similar structural descriptors such as void, pocket, hole, contact opening, via and the like. A radius of curvature r1 of the container corresponds to the radius of curvature of opening 18 of mask 12. To form a capacitor, container 19 is lined with first conductive material, dielectric, and second conductive material layers respectively.
In order to minimize costs, manufactures of DRAM""s strive to reduce the dimensions of the container-cell capacitors and increase the density of such cells within the array. Accordingly, some have developed a container-cell capacitor having a primarily rectangular cross-section for providing increased capacitance without sacrificing cell density. Referencing FIGS. 4A and 4B, such exemplary prior art container 19 comprises a cross-section of rectangular outline 23 offering an increase in the area of the container walls. This increased area, in-turn, increases the electrode area and capacitance value of the container-cell over that which might otherwise be provided by an equivalent width cylindrical container 18.
In a prior art method of forming a mask with a rectangular aperture, referencing FIGS. 5A and 5B, insulating material 10, e.g., BPSG, is layered over a silicon wafer of a supporting substrate 21. Etch resistant material 96 is layered over insulating material 10. Etch resistant material 96 is capable of resisting an etchant that is used during subsequent etching of insulating material 10, and may comprise, e.g., nitride of about 1,000 angstroms thickness. Photoresist (not shown) is layered over the top of etch resistant material 96 and patterned to define lateral apertures therein. The lateral apertures of the photoresist are used to define lateral openings 100 into etch resistant material 96. After forming lateral openings 100 in etch resistant material 96, the first photoresist is removed.
Continuing with this particular, exemplary, prior art method, additional photoresist 94 is applied over the patterned etch resistant material 96. This new photoresist is patterned to define longitudinal openings 106 that overlap lateral openings I 00, thereby defining rectangular openings 18 (FIG. 5B) at overlapping regions. Thereafter, select regions of substrate 21 are processed or etched in accordance with the openings to define containers 19. In this exemplary prior art method of forming a rectangular opening for a mask, the second photoresist is layered over the substrate and processed only after the first, lower photoresist has been fully processed. In other words, the lower photoresist is processed first, and only then is the upper layer of photoresist coated thereover and processed.
After forming this mask opening, the substrate is etched in accordance with the rectangular opening of the patterned photoresist and lower mask material, so as to provide a container within the substrate having primarily a rectangular cross-section corresponding to the rectangular opening of the mask.
In the above, exemplary, prior art method of forming a mask with a rectangular aperture, the upper photoresist is applied to the substrate only after the lower mask material has already been processed to define the lateral opening therein. In other words, the exemplary prior art sequence of steps comprises, in general, processing the first mask material, applying photoresist over the first mask material, followed by processing the photoresist. With this sequence of steps, the substrate is moved from, firstly, an etch or development station associated with processing the first mask material; to, secondly, a photoresist coat station for applying the photoresist over the processed mask material; and then back to, thirdly, an etch or resist development station to define the longitudinal openings in the photoresist. Recognizing a need in the manufacture of semiconductors to reduce handling and travel of wafers during semiconductor production flows, so as to reduce the time and costs associated with such wafer transport, the present invention proposes a new mask and method of manufacture thereof that can provide for effective and efficient semiconductor production flows.
Accordingly, the present invention provides a new mask and method of manufacture thereof, for use in forming a container for a container-cell capacitor having a rectangular cross-section, which mask and method of manufacture are capable of overcoming some of the above limitations. Furthermore, an array of containers are formed in a substrate by etching a substrate in accordance with fine geometry openings of such mask, providing for an efficient process flow.
In accordance with a first embodiment of the present invention, a method of forming a mask comprises layering radiation blocking material over a layer of first radiation sensitive material, such as photoresist. The radiation blocking material is patterned to provide a first opening therein that uncovers a portion of the layer of radiation sensitive material. Next, the layered structure is irradiated in accordance with an exposure pattern that overlaps a portion of the first opening, thereby irradiating a region of the lower radiation sensitive material. The radiation sensitive material is then developed to remove the irradiated region thereof and form an opening for the mask.
In accordance with one aspect of this embodiment, a second layer of radiation sensitive material, e.g., photoresist, is layered over the layer of radiation blocking material and patterned to provide a longitudinal opening therein and uncover a corresponding region of the radiation blocking material. A visible portion of the radiation blocking material is removed using the patterned, second layer of radiation sensitive material as a mask, thereby forming the first opening in the radiation blocking material.
Preferably, the second layer of radiation sensitive material is provided a longitudinal opening, and the lower layer of radiation sensitive material is irradiated using a lateral exposure strip that overlaps the longitudinal opening.
In accordance with one aspect of the invention, a DARC (dielectric antireflective coat) layer is provided between the light blocking material and the second photoresist.
In a further embodiment of the present invention, a mask, as outlined above, is formed over a substrate. Again, the second layer of radiation sensitive material has been patterned to provide a longitudinal opening, and lower layer of radiation sensitive material irradiated using a lateral exposure strip that overlaps the longitudinal opening to provide for a rectangular overlap region. The exposed, rectangular overlap region is developed to provide a mask aperture having a rectangular outline. Through this mask aperture, select regions of the substrate are etched to form a container therein with a rectangular cross-section corresponding to the rectangular outline of the mask aperture.
In accordance with one aspect of this embodiment, a capacitor is formed within the container, thereby providing a container-cell capacitor with a rectangular cross-section.
In accordance with yet another embodiment of the present invention, a mask comprises a layer of first photoresist, a layer of light blocking material over the first photoresist, and second photoresist over the light blocking material. A dielectric antireflective coat (DARC) is provided over the light blocking material and beneath the second photoresist. In accordance with one aspect of this embodiment, at least one of the first and second photoresists is patterned per a longitudinal exposure strip, and the other per a lateral exposure strip. The first one comprises an opening corresponding to the longitudinal exposure strip, and the other an opening corresponding to an overlap of the longitudinal and lateral exposure strips.